In recent years, a seatbelt buckle device includes therein a buckle switch which detects whether an occupant is buckled up, so that airbag deployment output, a seatbelt winding motor, and the like are controlled depending on whether the seatbelt is buckled. An example of a known buckle switch of this kind is provided with a fixed contact and a movable contact in the buckle and configured to allow the movable contact to slide into contact with the fixed contact as a tongue plate is inserted, so that whether the seatbelt is buckled/unbuckled is detected on the basis of a change in the contact. Such a device is described by Japanese Patent Application Publication No. 2009-240528.
For example, the conventional buckle switch 100 shown in FIG. 7 of the present disclosure includes a switch substrate 101 having a fixed contact 102 provided on one surface thereof (on the side of a frame 112) and a slider part 105 which has a movable contact (not shown) and moves by sliding on the switch substrate 101. The switch substrate 101 is positioned with its longitudinal ends being fitted in the grooves 111 of the lower case 110 and is arranged along one side wall 113 of the frame 112. A connecting part 106 which protrudes from the slider part 105 to the side wall 113 is engaged with the forked groove 116 of an ejector 115. The ejector 115 operates synchronously with detachment/attachment of the tongue plate (not shown) to be guided to the insertion hole 114 of the frame 112 and slide therein. The insertion of the tongue plate causes the ejector 115 to slide, so that the slider part 105 slides on the fixed contact 102 of the switch substrate 101 together with the movable contact, and the contact state is switched.
However, in the conventional buckle switch 100 shown in FIG. 7, the frame 112 having a plurality of buckle activating parts activated by the insertion of the tongue plate and the switch substrate 101 are fixed independently from each other in the lower case 110, so that during assembling of the buckle switch 100, the relative positions among the elements can vary, i.e., the frame 112, the switch substrate 101, and the lower case 110 should be adjusted to fall within tolerance ranges, which increases the man-hours for assembling. Since the frame 112 and the switch substrate 101 are provided independently from each other, the seatbelt buckle device may be relatively large. The switch substrate 101 is fitted and fixed in the grooves 111 of the lower case 110, so that wear debris generated by the sliding movement of the buckle activating parts, and sand and dust in the buckle may stick to the switch substrate 101, which may lower the contact resistance at the switch contact part (the contact point between the fixed contact 102 and the movable contact), and there has been a demand for a measure against the problem.
Since the fixed contact 102 is provided on the side of the frame 112 of the switch substrate 101, wear debris generated as the buckle activating parts slide easily sticks directly to the fixed contact 102, and the switch contact may catch foreign matter, which is more likely to cause a drop in the contact resistance.